How should you treat your tubes?

Here's some great advice from Kevin Deal @ Upscale Audio (www.upscaleaudio.com):

Tube Life, noise, and do I leave the power on -

We get asked this question a lot. With a power amp…you would typically not leave it running 24 hrs a day. Power amps produce heat, and they use a bit of electricity. Pre-amps, DAC’s and other products that use small tubes are another question. Regardless of what anyone tells you…I have not found a definitive answer to this question.

Tubes age in a couple ways. One is they lose emissions over their lifetime. In other words, they run out of gas. Or better yet steam…as they don’t just "quit" but lose their drive capability gradually. If you figure a tube like a 12AX7 or 6922 to be good for about 10,000 hours, and you leave it on 24 hours a day…well…you do the math. There are 8,736 hours in a year. So when did the tube go bad? It depends on how picky you are. It’s like a tube of toothpaste. Kinda peters out at the end but it seems you can squeeze out a little more. Some products (and audiophiles) are more picky than others. I recommend to folks that want to upgrade to premium new old stock tubes that they do it while their stock tubes are good. That way you have the cheap ones working and available should you decide to sell the pre-amp.

The other way they age is to become noisy. The noise will sound like popcorn popping softly in the background, or it may become a roar, and it can happen to any tube….including new ones. The most common reason that I have found for tube noise is the coating on the filament becomes compromised. This can be made worse by turning them on and off a lot. That’s the best way to guarantee trouble with tubes. Some products have filaments that are left on even when the product is turned off. This is a good idea and reduces that shock and keeps your pre-amp in a "warm" state. Other than that….maybe a mixture of a total power off if you will be gone a day or so, and leave it on when you anticipate you will be listening.

For a stretch of an hour or two, I would not turn off either, certainly not the preamp anyway.

Beyond that kind of time, a lot of different considerations come into play. Not only is the life of the tube at issue. Heat can damage other components, so leaving on tube gear, particularly if the tubes are enclosed or if you are dealing with hot output tubes, can result in shorter life for such components.

Other considerations include whether the equipment has "soft start" circuits (slowly brings up circuits so thermal stress on tube filaments are reduced) or if the power supply employs tube rectification (also results in slow turn on). With such slower turn on, the issue of wear from the turn on part of the cycle is reduced.

Probably the best answer would be that provided by the manufacturer.

Small signal tubes such as 12AX7's or 6922's are generally best left on 24/7. Quoting from the "TIPS & ADVICE" section of the owner's manual to my VAC Rennaisance 140/140 Mk. III tube amps:

"How long should tubes last? It has long been known in professional circles (and probably now forgotten) that a tube such as the 12AX7 will display BETTER performance characteristics after TWO YEARS of CONTINUAL operation than when it was new. In normal use it is not unusual for a low level tube to last 5 years or longer. Output tubes [i.e., power tubes used in tube power amps] are another story, as they are continuously providing significant amounts of current." (Emphasis original).

The expansion and contraction that small signal tubes undergo as gear heats up and cools down (as a result of being turned on and off) takes a toll over time. In addition, the voltage rush at turn-on is especially hard on small signal tubes. Tube gear with tube rectification is a lot easier on tubes at start-up, and some tube gear has a soft-start feature to soften the blow, while solid-state rectification is hard on them. In summary, while it is to a certain extent model-dependent, it's generally better, for both tube life and for sound quality, to leave tube preamps (and other gear that uses small signal tubes, like DAC's and tuners) on 24/7.

After a few years, the tubes should be replaced, as they do start to "lose their luster" (see Kevin Deal comments above), but they won't fail if used this way -- generally speaking, tubes left on 24/7 either fail within the first 250 hours or so from "infant mortality" or they last forever.

Output tubes cannot be left on 24/7 because they pass a lot of current and will wear out relatively quickly (not to mention wasting a lot of electricity and occasionally dying in spectacular fashion -- best not to leave them unattended).

Raquel,

That is interesting information from a manufacturer. But, how would one keep the small tubes (input, driver, phase splitter) of a power amp, like the VAC 140/140, on while the output tubes are not on? Does it have some sort of standby feature?

Also, while it is generally true that linestages have small signal tubes that don't degrade very rapidly under constant on conditions, that is not always the case. For example, the Counterpoint SA 3000 is pretty hard on tubes.

I might also be a bit leery about leaving on a linestage that had a lot of expensive small signal tubes in them (fortunately for me, my linestage uses cheap 12B4s for signal tubes). Still, I turn it off when not I am out for a long period of time. My phono stage has Telefunken ECC83s in it and uses two 300b tubes as rectifiers, I really hate to leave it on when not in use.